1. Field of the Invention
The present invention relates to an optical waveguide device and the like, in particular, to an optical waveguide device and a manufacturing method for an optical waveguide device with which accuracy and productivity improves when an optical device is mounted on a corresponding position of an optical waveguide.
2. Description of the Related Art
An optical transceiver used in an optical access market includes a module in a micro-optics type composed of an LD, a PD, a thin film filter, a lens, and the like, and a PLC module composed of a silica waveguide formed on a silicon substrate which is further mounted with an LD and a PD by hybrid mounting. The both have advantages and disadvantages. However, the latter is more advantageous in terms of a cost and delivery because it is less complicated than the former that needs to align optical axes of each component with monitoring an optical output. The latter utilizes a technique generally called passive alignment for the hybrid mounting.
In the passive alignment, a positional accuracy of a mounting component in a planar direction with respect to an optical waveguide section is secured by recognizing an image of an alignment marker formed on the mounting component. In addition, a positional accuracy in a vertical direction is secured according to a platform formed on the substrate. Since the height of this platform can be formed with high accuracy, a height thereof can be aligned with a height of the optical waveguide with high accuracy by only mounting the optical device on the platform.
FIGS. 12 and 13 show examples of an optical waveguide device constructed with the passive alignment. In the example shown in FIG. 12, an optical waveguide device 50 formed in a planar shape includes an optical waveguide forming section 56 formed on a substrate 51 made of silicon crystal, and an optical device mounting section 57 provided in response to the above. The optical waveguide forming section 56 is composed of an optical waveguide section 55 including a base layer 521, a lower cladding layer 522, an optical waveguide core 53, and an upper cladding layer 54, formed on the silicon substrate 51.
In addition, the optical device mounting section 57 is composed of an optical device 58 mounted so as to be coupled optically with an end face (a left end face in FIG. 13) of the optical waveguide core 53 which is exposed because the optical waveguide forming layer 55 is partially removed, and four platform blocks 59 for setting the height of the optical device 58 with high accuracy. Top end faces of each platform block 59 include chromium films 61. A semiconductor laser chip (LD) is used as the optical device 58. The optical device 58 is fixed on the platform blocks 59 in a condition where optical axes of an active layer 58A in the optical device 58 and the optical waveguide core 53 in the optical waveguide section 55 are aligned.
The optical device mounting section 57 includes the aforementioned platform blocks 59 formed with a same film as the base layer 521, and marker tables 60 provided with alignment markers (made of a chromium film, two of them are formed in right and left sides) on the top end face for adjusting a position. The platform blocks 59 are patterned from the same film with the base layer 521, so that the platform blocks 59 and the base layer 521 are in the same height. When the optical device 58 is mounted, the optical device 58 is supported on the platform blocks 59. The base layer 521, the lower cladding layer 522, the optical waveguide core 53, and the upper cladding layer 54 are formed with a CVD respectively.
Meanwhile, an alignment of the optical device 58 in the planar direction is performed by using two of the substrate side alignment markers 62 provided in the right and left sides in the optical device mounting area 57. The alignment marker tables 60 holding the substrate side alignment markers 62 is in a cylindrical shape, and fix the substrate side alignment markers 62 made of a metal film (a chromium film) thereon. A center position of the circle on the top surface of the substrate side alignment marker 62 is adjusted with high accuracy based on a position of the waveguide core 53 in the optical waveguide section 55.
As shown in FIG. 13, there are two of optical device side alignment markers 58a provided in a bottom surface of the optical device 58, corresponding to the substrate side alignment markers 62. The optical device side alignment markers 58a are, as shown in FIG. 14, formed as a metal film pattern in a circular punched shape, and the centers of the circles are arranged in the right and left sides and aligned with high accuracy based on a position of the active layer 58A in the optical device 58. Further, positions of the optical device side alignment markers 58a and the substrate side alignment markers 62 are specified so that the optical device 58 is placed in a right position to be fixed when the centers of those optical device side alignment markers 58a and the substrate side alignment markers 62 are matched with each other.
When the optical device 58 is actually mounted as shown in FIGS. 12 and 13, the metal film patterns in the optical device 58 side (the optical device side alignment markers 58a) and the substrate side alignment markers 62 are superimposed by the image recognition as shown in FIG. 14. In this case, infrared light is emitted from the substrate 51 side, as shown in FIG. 13, and a monitoring camera 52 disposed upward monitors transmitted light. Consequently, images as shown in FIG. 14 can be obtained because the metal part shields the infrared light.
The diagram in the left side in FIG. 14 shows a case in which the center axes of the substrate side alignment markers 62 and the LD side alignment markers 58a are not aligned with each other on the substrate 51 when the optical device 58 is going to be mounted. Further, the diagram in the right side in the same figure shows a case in which the center axes of the substrate side alignment markers 62 and the LD side alignment markers 58a are aligned.
Each position of the substrate side and the optical device side alignment markers 62, 58a are specified with high accuracy with respect to the positions of the waveguide core 53 in the optical waveguide section 56 and the active layer 58A of the optical device, respectively. Therefore, if the optical device is mounted on a position where the center of the circles for both are aligned, optical axes of the active layer 58A and the optical waveguide core 53 in the planar direction can be aligned with high accuracy.
As for the optical waveguide device of this type, a technique disclosed by Japanese Patent Application Laid-open No. 2002-062447 (Patent Document 1) has been known. In the technique, as alignment markers, short linear markers parallel to the optical axis are formed at the position where each end face of the optical waveguide section and the optical device section are abutted, and alignment is performed at the position the markers are abutted and matched. According to the technique, the optical waveguide section and the optical device section can be aligned while both are abutted. Therefore, the alignment can be performed by the adjustment in a direction along with the end faces of those only, and two-dimensional alignment is not required.
As shown FIGS. 12 and 13 with respect to the aforementioned related art, in order to make it possible to align each optical axis of the optical waveguide core 53 and the active layer 58A in the optical device side according to the alignment of the center axes of the optical waveguide side alignment markers 62 and the optical device side alignment markers 58a, it is required that the centers of each marker corresponding to the waveguide core 53 side (or the active layer 58A side in the optical device 58) are specified with high accuracy in advance.
Meanwhile, when the optical waveguide device is mass-produced, a number of optical waveguide chips are produced on a silicon wafer at the same time. The silicon wafer processing includes a lot of processes in which the whole wafer is stressed with a thermal process, a film formation, and the like. Therefore, when the substrate side alignment markers 62 provided in the optical device mounting area 57 and the optical waveguide core 53 provided in the optical waveguide section 55 are patterned respectively, the accuracy of position adjustment for both are different in some cases due to variations of distortion degree in the wafer. Further, the optical waveguide core 53 and the corresponding substrate side alignment markers 62 are formed in different layers, and their position adjustments are performed in different processes respectively. Therefore, their relative positions are depending on the accuracy of each position adjustment, and the positions thereof are not always stabilized. An example of this case is shown in FIG. 15.
In FIG. 15, the optical waveguide core 53 and the substrate side alignment markers 62 are provided on the same substrate 51. Further, both of the active layer 58A and the optical device side alignment markers 58a are provided in the optical device section 58 (refer to FIGS. 12 and 13). X marks in FIG. 15 express, in the optical device mounting area 57, proper positions in which the substrate side alignment markers 62 are supposed to exist (theoretically). On the other hand, actual positions of the substrate side alignment markers 62 are recognized by the monitoring camera and the like, which are shifted in some cases from the points expressed by X marks.
This is because the accuracy in the position adjustment varies due to the distortion of the wafer caused by the stress when each section in a module is patterned. Therefore, when the optical device 58 is mounted after the centers of the substrate side alignment markers 62 are aligned with the centers of the optical device side alignment markers 58a according to the method in the case of FIG. 14, a problem can occur where the optical axes of the waveguide core 53 and the active layer 58A are not aligned with each other as shown in FIG. 15. However, in the aforementioned example, there is no way to detect proper positions in which the substrate side alignment markers are supposed to exist. Therefore, it is impossible to know how much the misalignment amount is, and, in addition, it is impossible even to judge whether there is the misalignment or not. Accordingly, an output rate of non-defective products is declined because of the trouble accompanied by the optical device mounting.
The technique disclosed in Patent Document 1 is suitable for the position adjustment only in a direction along with the end faces where the optical waveguide section and the optical device section are matched. However, various transformations practically occurs in the substrate, the device section, and the like, which are caused by distortion due to a problem of processing accuracy or stress. Accordingly, the two-dimensional position adjustment including angular adjustment is required when the optical device section is to be mounted. It is very difficult for a one-dimensional linear alignment marker to perform this adjustment. For example, a big problem occurs if an optical axis of an optical waveguide is misaligned even by 1-2 degrees, however, such a small misalignment cannot be recognized practically with an alignment marker having a length far shorter than the optical waveguide. Further, the length of the alignment marker cannot be extended because an image needs to be within a screen of a monitor for the alignment. Therefore, this technique is not efficient in any alignment other than the one-dimensional alignment.